The president, on a strict new diet and exercise regime, did not lose consciousness but needed to lie down, said officials, contradicting earlier reports that he had fainted.

It had been reported that he had suffered vasovagal syncope - a nerve condition in which exhaustion and dehydration can lead to a loss of consciousness due to a loss of blood pressure. But it seems he actually suffered a vasovagal episode, which is less intense.

A cardiologist at the Georges Pompidou Hospital in Paris was reported as saying that such episodes were caused by a fall in arterial pressure and heartbeat frequency, therefore slowing the blood flow to the head.

So what are the health hazards associated with jogging?

The benefits far outweigh the risks, says Andy Dixon, editor of Runner's World magazine, and it's very rare to hear about the kind of vasovagal episode experienced by Mr Sarkozy.

THE ANSWER

Benefits far outweigh risks

Road running can cause pain to joints

Fainting is rare but can be prevented by drinking water and warming down

"It seems to have been triggered by a combination of the exertion of running, the strict diet he was on and dehydration from the heat," he says.

Two ways to prevent this would be to hydrate your body while running - but not too much - and warm down properly afterwards so that the heart rate, blood supply and the muscles can return to normal.

"The current advice is to drink only when you feel thirsty, because the body acts like a sophisticated sensory device and you'll get a dry mouth and feel dehydrated when you need to drink.

"And at the end of a run, rather than just stopping dead, it's better to run a bit more slowly and slow down until walking fast, allowing the body to adjust gradually back to rest."

BENEFITS OF RUNNING

Increased fitness levels

Good for weight control

Heightens sense of well-being

Reduces long-term risk of cardiac problems

Good way to explore a city or enjoy the countryside

Source: Runner's World

A more common complaint among runners than fainting is the impact on joints, says Mr Dixon, although the risks should not be exaggerated.

"It's a high-impact activity but the more you do it, the stronger your joints get. There's a fallacy that it wrecks your knees and ankles but there's a long-term study that says the more you do it, it ends up strengthening them."

"These are generally wear-and-tear injuries," says Mr Dixon, who says he has never experienced any of them himself.

RUNNING SAFELY

Don't overdo it - faster than a walk is sufficient for a beginner

Don't use an iPod when running in the street or road because you need to be attuned to your environment

Scan the ground in front of you to detect uneven surfaces

Source: Runner's World

"A period of rest is usually the solution, for two to three weeks until the pain you're feeling, which is usually a dull pain while running, disappears."

There have been reports of runners suffering fatal heart attacks but there is usually an underlying cardiac condition which is triggered by running, not caused by it, he says.

There's a paradox that people are more likely to suffer a heart attack while running than watching television, he says, but people who run regularly are 50% less likely to have a cardiac episode than someone who has a sedentary lifestyle.

The impact on joints is greater for people with heavier builds, says personal trainer Ryan Bull, of Paris Gym in south London.

People who intend to take up jogging should start on a treadmill, which is not as punishing as the road, he says, and setting the treadmill at an incline of 1% is a good idea because jogging uphill lessens the impact on the knees and replicates more closely the slopes of the streets.

WHO, WHAT, WHY?

A regular part of the BBC News Magazine, Who, What, Why? Aims to answer some of the questions behind the headlines

"Injuries can happen but they shouldn't stop people from doing it. After three or four weeks on the treadmill, changing the incline, then go outside but start on soft ground like the park.

"It's a good idea to first walk the route on the streets where you want to jog, rather than aimlessly going out, because things like potholes in the road can cause injuries."

And if your aim is to lose weight, he says, then regularly walking uphill at a brisk pace for more than 15 minutes can be the most effective way of achieving that.

Below is a selection of your comments.

Don't get carried away by your own assumed fitness. As a 30-something back in the 1980s, I jogged about 2 miles every weekday and 5 miles on Sunday morning, which was a glorious way to enjoy the countryside around where I live, and I was as fit as a fiddle. Then, one day in January 1989 I pulled up short with an excruciating pain in my knee. This was diagnosed immediately as chronic arthritis and I was ordered to stop the activity since it would only make it worse. The condition spread to all my joints. Nowadays, I can't even walk fast. So take care. Pain doesn't always mean gain.Tony Cooley, Walsall

Running is not the best form of exercise and is damaging to joints, despite what the editor of Runner's World might have to say - hundreds of people every year need knee cartilage operations as a result of running on tarmac. My uncle, who was a top marathon runner in his day, is now almost crippled at the age of 65 due to joint damage. If you are looking to keep fit, far better to go for a bike ride or swim etc. If you must go for a run, keep to soft ground.Helen, UK

As a 54-year-old runner living near Versailles, I would suggest to Mr Sarkozy that he tries running earlier in the day than 1pm if it is as hot as yesterday. At 8.30am it was already sufficiently warm to be becoming uncomfortable after 45 minutes.Peter Fox, Montigny-le-Bretonneux, France

Interesting that Sarkozy is on a strict diet - that's not conducive to healthy running - I swear by a pre-run bowl of porridge with a little honey accompanied by a big glass of water.Kate, Bristol

The best way to run everyday for many years without injuring oneself are: 1. Run at the pace you are comfortable with 2. In extreme or new weather, work out with right clothing and consume water before you feel thirsty 3. Increase speed or mileage only 10% over previous week - don't run 10 miles if you have done only 6 miles for many weeks 4. Stretch before and after run/jog for 10 minutes 5. Work out strength training 3 days a week to keep the quads, hamstring stronger which will avoid any knee, calf, ankle injuries 6. Don't run after heavy drink previous night 7. Check your shoes and change when worn out. use the shoe one size bigger than your size.Sridhar, Bangalore, India

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